A Silurian Ark was a large starship, roughly as wide as Canada, created by the Silurian civilisation during the final days of their rule to ensure the survival of their race when their civilisation was threatened with extinction.
The large, roughly spherically shaped craft was able to hold thousands of crew in hibernation pods and an entire self-contained ecosystem for animals to thrive. Some parts resembled outside planetary environments that were a near perfect replica of an environment, though a keen observer was able to sample the air and detect metallic content therein. Another example of the ship's true nature was present in these environments as underneath the soil and sand were metallic plates. Its engines were powered through hydroelectric means with a large ocean that used waves as a form of energy.
A computer system allowed easy access to information and included a teleport system to any area of the ship. The control deck served as the command centre for the entire ship and included an automated piloting system that locked the target for the vessel. Piloting of the ship involved parallel pilot compartments — chairs that required the users to be of the same gene chain. (TV: Dinosaurs on a Spaceship)
This craft's creation was dated to the end of the Silurians' rule of the planet Earth. At the time, they discovered an object that was forecasted to collide with their home-world. The majority of their race entered into suspended animation though some of their kind created a large spaceship designed to hold their people and a large number of dinosaurs to find a new world to colonise.
The Ark travelled in space where the preserved dinosaurs managed to thrive except for one species. Whilst in hibernation, the Ark was boarded by Solomon, a pirate who determined its cargo to be of high value that he could sell. After boarding the ship, he had his two robots wake up a few of the Silurians at a time and disposed of them when they refused to give him the dinosaurs. A whole crew of thousands was killed this way. Due to the piloting method of the ship, Solomon was unable to control the ship and it automatically returned to Earth.
In 2367, the Ark's path toward Earth prompted the Indian Space Agency to identify it as a threat. Accordingly, the ISA planned to destroy it with a barrage of missiles. In this time, the Eleventh Doctor learnt of the ships existence and was determined to save it. He took Queen Nefertiti, John Riddell, Amy Pond, Rory Williams and, accidentally, Brian Williams to the ship where he encountered Solomon.
Being a father and son, Brian and Rory were able to operate the parallel pilot compartments and steer the Ark away from Earth. At the same time, the Doctor placed the Ark's signature onto Solomon's ship causing the missiles to target it vice the Ark. Solomon was forced to witness his own demise as the missiles crashed into his ship. The Ark and Earth safe, the Doctor and Brian fulfilled the Silurians' plans, establishing a planetary refuge for the dinosaurs, which they dubbed Siluria. The Ark was presumably abandoned afterwards. (TV: Dinosaurs on a Spaceship)
Numerous Silurian Arks were seen above Trenzalore during the Siege, having travelled there in response to the First Question. They either retreated from the planet or burned in the fighting after the Daleks broke through the Papal Mainframe's force field and plunged Trenzalore into war. (TV: The Time of the Doctor)
Alternate timeline Edit
The Cybermen converted Silurian Arks and used at least one of them to create Cyber-Silurians. Later the Cyber-Arks were launched to attack the CyberKing controlled by the Tenth Doctor. (COMIC: Supremacy of the Cybermen)